Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $63.94   7.327%   $68.6249   $68.62   $68.60   $68.60  
  Purchase #2 $131.59   5.134%   $138.3458   $138.35   $138.35   $138.30  
  Purchase #3 $213.51   9.260%   $233.281   $233.28   $233.30   $233.30  
  Purchase #4 $42.86   8.563%   $46.5301   $46.53   $46.55   $46.50  
  Purchase #5 $249.90   4.587%   $261.3629   $261.36   $261.35   $261.40  
  Purchase #6 $101.30   6.248%   $107.6292   $107.63   $107.65   $107.60  
  Purchase #7 $78.29   11.719%   $87.4648   $87.46   $87.45   $87.50  
  7 purchase totals = $881.39       $943.2387   $943.23   $943.25   $943.20